CREATE TABLE TEST_LOOP
(ID1 NUMBER,
ID2 NUMBER);


INSERT INTO TEST_LOOP VALUES (1,2);
INSERT INTO TEST_LOOP VALUES (2,2);


INSERT INTO TEST_LOOP VALUES (3,4);
INSERT INTO TEST_LOOP VALUES (4,3);

INSERT INTO TEST_LOOP VALUES (5,6);
INSERT INTO TEST_LOOP VALUES (6,7);
INSERT INTO TEST_LOOP VALUES (7,7);

INSERT INTO TEST_LOOP VALUES (9,10);
INSERT INTO TEST_LOOP VALUES (10,11);
INSERT INTO TEST_LOOP VALUES (11,12);
INSERT INTO TEST_LOOP VALUES (12,12);

COMMIT;


SELECT id1,id2,PRIOR id2 ,CONNECT_BY_ISCYCLE loop
FROM TEST_LOOP
START WITH id1 in (1,3,5,9)
CONNECT BY nocycle    PRIOR id2=id1;

   SELECT id1,id2,PRIOR id2, level lv
     -- , CONNECT_BY_ISCYCLE loop
     FROM TEST_LOOP
    START WITH id1 in (1,3,5,9)
  CONNECT BY --NOCYCLE
    PRIOR id2  = id1 
AND PRIOR id1 != id2;

ID1   ID2  PRIORID2   LV
-------------------------------
1	2		1
2	2	2	2
3	4		1
5	6		1
6	7	6	2
7	7	7	3
9	10		1
10	11	10	2
11	12	11	3
12	12	12	4